General Motors has seen the writing on the walls when it comes to efficient vehicles. Although gas prices have dropped more than 15 cents in the past few weeks, Americans are still gravitating towards smaller vehicles that are easier on the wallet when the times comes to fill up the tank.

GM has spent the past few years working on a number of technologies to bring lightweight, advanced, and fuel efficient powertrains to its vehicles and a number of them are already available or will soon be hitting the general populous.

GM's reinvigorated powertrain efforts revolve around traditional gasoline engines, diesels, hybrids, and Homogeneous Charge Compression Ignition (HCCI) engines according to Automotive News. GM is also looking to replace nearly all of its existing four and five-speed automatic transmissions with more efficient six-speed units.

For its gasoline engines -- much like Ford's efforts with its EcoBoost lineup -- GM is looking towards direct injection (DI) and turbocharging to extract V6 performance from four-cylinder engines and V8 performance from six-cylinder engines. GM's current turbocharged DI 2.0-liter four-cylinder engine can be found in the Pontiac Solstice GXP, Saturn Sky Red Line, Chevrolet HHR SS, and the Chevrolet Cobalt SS. In its current form, the engine delivers an impressive 260 HP and 260 lb-ft of torque.

In the near future, GM will apply turbocharging to its existing DI 3.6-liter six-cylinder engine to boost output from roughly 300 HP to around 400 HP. On the lower end of the spectrum, a new 1.4-liter turbocharged four-cylinder engine will finds its way into the Chevrolet Cruz -- the replacement for the Chevrolet Cobalt -- in place of the existing 2.2-liter normally aspirated (NA) four-cylinder engine.

On the diesel front, GM points to its upcoming 4.5-liter V8 diesel engine which will be used in its light-duty pickups and full-size SUVs. According to GM, the engine itself is 75 pounds lighter than traditional diesel engines and will allow its hefty trucks to achieve 26 MPG on the highway.

When it comes to hybrids, GM is already making ground with its mild hybrid system in the Chevrolet Malibu Hybrid and Saturn Aura Green Line. Eventually, the company's more efficient two-mode hybrid system -- currently used in full-size pickups and SUVs -- will find its way into the Saturn Vue Green Line and GM's other mid-size cars and SUVs.

Finally, GM is also banking on HCCI technology to extract diesel-like fuel economy from a gasoline engine. DailyTech first brought you news of this technology when Mercedes unveiled its F700 research vehicle. According to GM, adding HCCI to a gasoline engine boost fuel economy by 15 percent and significantly reduced harmful tailpipe emissions.

GM hopes to stay a step ahead of its competitors with its upcoming powertrain advances; however, its competitors likely aren't sitting still when it comes to their own efforts in striving for greater performance and engine efficiency.